Molecular characterization plays an important role in understanding the function of chemical processes that occur in biological systems and has provided a unique contribution to biochemistry and medicine. High sensitivity and the ability to examine complex mixtures have greatly extended the role of chemical methods in medicine in diverse roles such as clinical monitoring of therapeutic drugs, drug metabolites and toxic molecules, studying trace levels of immunosuppressive proteins, protein and DNA sequencing, etc. Thus, improved method for obtaining structural information and quantitation of large biomolecules, particularly those present at trace levels and in complex mixtures, will make possible new experiments and enhance our ability to solve problems of biomedical interest. One of the goals of the proposed research is to improve the sensitivity of electrospray ionization with Fourier-transform mass spectrometry (FTMS). Methods to explore the mechanism of ion trapping, and improvements in sample duty cycle are proposed. The combination of capillary electrophoresis with FTMS will be used to investigate unknown classes of neurotransmitters and neuromodulators. A new method to measure electrostatic forces in peptides and proteins is proposed. The gas-phase basicity of multiply protonated ions is used as a quantitative probe of Coulomb repulsion. From these measurements and estimates of distance between charges, accurate values for the intrinsic dielectric polarizability of peptide and proteins can be obtained. This value is of key importance in understanding processes in which electrostatic forces play a role, such a protein folding, intramolecular electron transfer, and dissociation of multiply protonated ions. This use of this method to obtain information about protein conformation in the gas-phase will be investigated. Protein ions will be probed for biological activity in the gas-phase as an indicator of their conformation.